Beaver Valley corrosion may mean wider problem
The corrosion found in April on Beaver Valley-1’s containment liner could be indicative of a wider problem, as two other reactors that operated under similar atmospheric conditions experienced problems in recent years, according to Pittsburgh-based interest group Citizen Power.
Theodore Robinson, the group’s staff attorney, told NRC’s Advisory Committee on Reactor Safeguards, or ACRS, in an August 27 letter that Beaver Valley-1, North Anna-2 and Surry-2 — three of the country’s six three-loop, subatmospheric nuclear reactors, which operated with a fraction of normal atmospheric pressure in their containment buildings — have experienced liner corrosion. And in addition to the April discovery at Beaver Valley, three points of liner corrosion were encountered at the plant during a steam generator replacement in 2006.
The affected reactors’ sister units — Beaver Valley-2, North Anna-1 and Surry-1 — account for the other three three-loop subatmospheric nuclear reactors.
“Only two out of 97 plants that have not utilized a threeloop sub-atmospheric design have experienced similar [corrosion] problems,” he said.
Arnold Gundersen, a nuclear engineer retained by Citizen Power, said in an August 26 interview that until recently utilities operated the containment buildings at Beaver Valley-1 and -2, North Anna-1 and 2, and Surry-1 and -2 at subatmospheric pressures for at least two decades. He said the inside of the containment buildings were kept at roughly two-thirds of normal atmospheric pressure as a safety measure. “If there was less mass — less oxygen — in the containment when you had a rupture or loss of coolant, you could recover and eliminate off-gassing from the containment very quickly,” he said.
Gundersen said utilities stopped operating containment buildings at subatmospheric pressure in recent years because the conditions were hot and uncomfortable for workers. Gundersen said he also believes the operating conditions could have increased the gap between the metal containment liner and its concrete shield, potentially providing space for oxygen and moisture to corrode the liner over time.
But Todd Schneider, spokesman for Beaver Valley operator FirstEnergy Nuclear Operating Co., disagrees that subatmospheric operating conditions are to blame for the corrosion found in April. He said August 27 that corrosion was not discovered when visual inspections were performed after the Beaver Valley reactors stopped operating at subatmospheric conditions in 2006. He said there has been no evidence of uniform corrosion on the liner and that the April 2009 discovery was at a specific point corroded by wood left behind during construction. Beaver Valley-1 began commercial operation in l976.
Since the discovery in April, Fenoc has repaired and tested the liner and plans to perform random sampling with ultrasonic testing, or UT, of the liner and visual inspections of the entire liner, he said late last month (INRC, 3 Aug., 3).
Robinson, however, wants Fenoc to inspect Beaver Valley’s liner more aggressively. “We strongly recommend that Advisory Committee on Reactor Safeguards find that UT testing should commence immediately and that either 100% of unit 1’s containment liner be tested or that FENOC modify the testing methodology to reflect the prior existence of corrosion,” he said in the letter.
And while Citizen Power is not focusing its attention on North Anna or Surry because they are in Virginia and not Pennsylvania where the group is headquartered, Gundersen said he believes their containment buildings should be ultrasonic tested as well to ensure the liners are sound. “Something’s fishy here, and we should make sure that those six containments haven’t developed something that was unanticipated,” he said.
Fenoc is scheduled to present its inspection plans to the ACRS in a September 10-12 meeting that among other issues will include an update on Beaver Valley’s license renewal application and supplemental safety evaluation report. Fenoc in August 2007 applied for a 20-year license renewal for both Beaver Valley units.
The NRC staff and Fenoc have to agree on an inspection approach before they present the plan to the ACRS, NRC staffer Kamal Manoly said August 26. Manoly, who has participated in conference calls with Fenoc over the liner corrosion, said the NRC staff is aware of Citizen Power’s concerns and will consider them internally as it develops Fenoc’s liner inspection plan.
Used with permission from The McGraw-Hill Companies, Inc.
Copyright © 2009, The McGraw-Hill Companies